This application claims the benefit of provisional application Ser. No. 60/554,661 filed Mar. 19, 2004.
The present invention is directed to soy protein-based adhesives useful in the manufacture of particleboard and other composites. The present invention is also directed to particleboards made with such adhesives.
Soy protein was used as an adhesive ingredient in plywood in the early 1900s. However, the problem of low moisture resistance led to its replacement with petroleum-based resins in the 1930s. Particleboard composites were subsequently developed that utilized urea-formaldehyde, phenol formaldehyde or polymeric methylene diisocyanate resins to bind the wood particles rather than agricultural adhesives.
However, increasing environmental awareness and the recognized hazards of formaldehyde-based adhesives has created a strong demand for more environmentally friendly wood adhesives. Successful replacement of urea formaldehyde resins in particleboard requires an adhesive that can produce composites having characteristics matching or exceeding those attainable with urea formaldehyde. Accordingly, water resistance is a necessary characteristic of any suitable replacement.
Soybean proteins are a combination of 18 amino acids of wide chemical diversity such as amines, carboxylic acids, hydroxyls, and mercaptan functionalities. Each of these functionalities is polar in nature and contributes to water sensitivity. Accordingly, in order to use soy protein as an effective adhesive, it is necessary to counteract and overcome this sensitivity. Additionally, the soybean binder must be chemically transformed into a hydrophobic adhesive without creating toxic by-products and/or waste streams.
Commercial particleboards are constructed in a range of thicknesses and are designed to have high-density surfaces and low-density cores so as to maximize strength while minimizing weight. Panel thickness for particleboards generally range from ½1 inches with ⅝ and ¾ inches being the most common thicknesses in the industry. Particleboard is classified and evaluated according to the ANSI A208.1 requirements and ASTM D-1037 tests are used to determine the physical strength and water resistance properties.
Particleboards are formed by mixing together wood furnish and an adhesive binder and treating the mixture under high temperatures and pressures in a press. Generally, binder concentrations of 7–10% are used to make particleboard. Accordingly, the wood furnish is considered to be spot welded together rather than imbedded within the adhesive. Consequently, the ASTM D-1037 test results often exhibit a coefficient of variance in excess of 10%.
In view of the foregoing, it would be a significant advancement in the art to provide an agriculturally-based adhesive that could be utilized to replace urea formaldehyde resins in particleboard and other composites. It would be a further advancement in the art if such an adhesive was primarily based upon renewable resources. Such an adhesive as well as particleboards made from these adhesives are disclosed and claimed herein.